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Diffstat (limited to 'Documentation/filesystems/overlayfs.rst')
| -rw-r--r-- | Documentation/filesystems/overlayfs.rst | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 5b93268e400f..0407f361f32a 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -344,10 +344,11 @@ escaping the colons with a single backslash. For example: mount -t overlay overlay -olowerdir=/a\:lower\:\:dir /merged -Since kernel version v6.5, directory names containing colons can also -be provided as lower layer using the fsconfig syscall from new mount api: +Since kernel version v6.8, directory names containing colons can also +be configured as lower layer using the "lowerdir+" mount options and the +fsconfig syscall from new mount api. For example: - fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir", "/a:lower::dir", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/a:lower::dir", 0); In the latter case, colons in lower layer directory names will be escaped as an octal characters (\072) when displayed in /proc/self/mountinfo. @@ -416,6 +417,16 @@ Only the data of the files in the "data-only" lower layers may be visible when a "metacopy" file in one of the lower layers above it, has a "redirect" to the absolute path of the "lower data" file in the "data-only" lower layer. +Since kernel version v6.8, "data-only" lower layers can also be added using +the "datadir+" mount options and the fsconfig syscall from new mount api. +For example: + + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l1", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l2", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l3", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "datadir+", "/do1", 0); + fsconfig(fs_fd, FSCONFIG_SET_STRING, "datadir+", "/do2", 0); + fs-verity support ---------------------- @@ -504,6 +515,29 @@ directory tree on the same or different underlying filesystem, and even to a different machine. With the "inodes index" feature, trying to mount the copied layers will fail the verification of the lower root file handle. +Nesting overlayfs mounts +------------------------ + +It is possible to use a lower directory that is stored on an overlayfs +mount. For regular files this does not need any special care. However, files +that have overlayfs attributes, such as whiteouts or "overlay.*" xattrs will be +interpreted by the underlying overlayfs mount and stripped out. In order to +allow the second overlayfs mount to see the attributes they must be escaped. + +Overlayfs specific xattrs are escaped by using a special prefix of +"overlay.overlay.". So, a file with a "trusted.overlay.overlay.metacopy" xattr +in the lower dir will be exposed as a regular file with a +"trusted.overlay.metacopy" xattr in the overlayfs mount. This can be nested by +repeating the prefix multiple time, as each instance only removes one prefix. + +A lower dir with a regular whiteout will always be handled by the overlayfs +mount, so to support storing an effective whiteout file in an overlayfs mount an +alternative form of whiteout is supported. This form is a regular, zero-size +file with the "overlay.whiteout" xattr set, inside a directory with the +"overlay.whiteouts" xattr set. Such whiteouts are never created by overlayfs, +but can be used by userspace tools (like containers) that generate lower layers. +These alternative whiteouts can be escaped using the standard xattr escape +mechanism in order to properly nest to any depth. Non-standard behavior --------------------- |